fox: There is no difference between slapt-get and gslapt. gslapt is just a GUI front end for slapt-get.
Yes, you can install rpms into Vector Linux but that is the LAST thing you want to do in this case. Installing from third party sources breaks dependency tracking and the package database on your system won't know about it.
Any file ending in .so.1 is a part of a package but not a package itself. Somehow you are missing a dependency and I don't know how that happened.
1. Uninstall rhythmbox using gslapt.
2. Make sure you have all of the following repositories enables:
packages, extra, patches, gsb, testing
Normally you wouldn't want testing enabled but in this case I want to make sure something you need isn't still in testing. Also, I had testing enabled when I installed and it worked.
3. Click the Update icon to refresh your package list from the repos.
4. Reinstall rhythmbox using gslapt.
See if that works.